As Fabien points out, the MapQuest FindMe (integrated with AIM) is a clever service that allow users to use manual sharing of one's position. Which is one of the guidelines that would emerge from our CatchBob! experiments. Self-disclosing one's location seems to emerge as a good trend now, both in the real world of services and the academic world of research as in those papers:

Nova, N., Girardin, F. & Dillenbourg, P.: ‘Location is not enough!’: an Empirical Study of Location-Awareness in Mobile Collaboration. Proceedings of the third IEEE International Workshop on Wireless and Mobile Technologies in Education, November 28-30, 2005, Tokushima, Japan, pp. 21-28, IEEE Press: Los Alamitos, California.
Benford, S., Seagar, W., Flintham, M., Anastasi, R., Rowland, D., Humble, J., Stanton, D., Bowers, J., Tandavanitj, N., Adams, M., Farr, J. R., Oldroyd, A., and Sutton, J. (2004). The error of our ways: The experience of self-reported position in a location-based game. In Proceedings of the the 6th International Conference on Ubiquitous Computing. (UbiComp 2004), pages 70–87, Nottingham.

Both paper advocate for self-disclosure of location. They rely on different approach to come up with this recommendation. Benford's paper has a qualitative approach and is more focused on users' thoughts. Whereas ours is more mixed-methods (quantitative methods dominant though), it proposed the same idea because of the underwhelming effects of automatic location-awareness on how people collaborate. Another paper for a conference about 'designing for collaboration' will deal with this issue.

I am still digging this issue of location-awareness on collaboration, working on both asynchronous location awareness and the importance of letting people express their own strategy.